12 April, 2010: The railway debris flow of South Tyrol

12. April 2010 South Tyrol: 9 confirmed victims, 23 people injured; this was the headline about a rail crash between the towns of Latsch and Kastelbell reported by the news almost worldwide.The modern railway between the two localities follows the orographic right bank of the main river Etsch, the accident occurred at a segment inside a gorge eroded by the river in Holocene sediments (manly a large alluvial fan coming from south with unconsolidated debris-flow deposits).At 9.02 in the morning, just when the train approached, a debris flow of 400 cubic meters - with a width of 10 to 15 meters and a thickness of 2m - bursted off 50m above the railway line and hit the first wagon, knocking it from the railway.

Fig.1. The derailed train during the difficult rescue efforts (SüdtirolNews).

To clarify possible causes of the landslide soon after geological investigations were initiated. Eye witnesses reported large quantities of water running down the slope after the accident. A preliminary site investigation by the authorities concluded that the leakage of an irrigation system above the location (the area is used for agriculture) saturated the soil and underlying sediments with water, causing a mudslide just in the moment the train passed. The irrigation system was in use since the previous week and at least for the last days or hour's large quantities of water infiltrated in the underlying slope and saturated the debris. It is possible that the vibrations of the approaching train triggered finally the fatal slide that initiated the debris flow.